Its either gonna be a earth leakage on the green wire at the CDI, normally caused by a chaffed wire somewhere or a knackered ignition switch. Easily checked with a multimeter on resistance Ohms checking, the wire should ONLY have continuity to earth (the frame) with the ignition off... if its got any continuity with earth with the ignition on then youve found the problem.. If not then its the stator windings that have failed... not hard to change, worst bit is sometimes the 5mm screws around the cover corrode in and snap off... nothing to hard to sort though. Only a few screws and the centre nut, ideally a puller to get the flywheel off, and then its just unbolt, replace and refit. Nothing anyone should be worried about attempting.
